Field of the Invention
The present invention relates to heavy duty pneumatic tires, and in particular relates to a heavy duty pneumatic tire capable of suppressing uneven wear.
Description of the Related Art
Japanese Unexamined Patent Application Publication No. 2009-234362 discloses a heavy duty pneumatic tire that includes a wide tread portion provided with a circumferentially and continuously extending shoulder rib, a first middle block row located axially inward of the shoulder rib and a second middle block row located axially inward of the first middle block row. The first middle block row includes blocks and lateral grooves which have the same circumferential length as blocks and lateral grooves of the second middle block row, respectively.
Generally, when heavy duty pneumatic tires are inflated, outer diameters of the tread portions grow. The outer diameter growth tends to occur largely around tread edges on which relatively low hoop effect of the belt layer acts. Thus, conventional heavy duty pneumatic tire tends to deform such that the first middle block row has a larger outer diameter than that of the second middle block row when inflated.
When the blocks and lateral grooves of the first middle block row have the same circumferential length as the blocks and lateral grooves of the second middle blocks respectively, a block occupying ratio in one pitch of the first middle block row reduces as compared with the second middle block row due to inflated deformation as mentioned above. Since the first middle block row as mentioned above has relatively low pattern rigidity, the first middle block row tends to wear earlier than the second middle block row. Note that the above-mentioned one pitch means one of repeated pattern elements including adjacent one block and one lateral groove.